JPH0634606Y2 - Pilot injection device for fuel injection pump - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application] The present invention is directed to a pilot injection device for a fuel injection pump, which is arranged in communication with a pressurizing chamber of the fuel injection pump and performs pilot injection prior to main injection of fuel. Regarding

[Prior Art] Conventionally, for the purpose of reducing combustion noise and improving ignitability of a diesel engine, pilot injection is executed prior to main injection of fuel by a fuel injection pump, and fuel from the pilot injection is ignited in a combustion chamber of the diesel engine. There is known a pilot injection device of a fuel injection pump that performs main injection at the time.

As such a technique, for example, "a pressure buildup temporary interruption device for a fuel injection pump" (Japanese Patent Laid-Open No. 61-129456) has been proposed. That is, when the fuel in the pressure chamber pressurized by the plunger of the fuel injection pump escapes to the expansion chamber when the pressure relief member biased by the spring retreats at a predetermined level pressure or more, the fuel is intermittently blocked by the plunger. And a bypass extending between the bypass hole and the expansion chamber, and the bypass hole is arranged so as to be kept open without being obstructed by the plunger at the non-injection timing. .

[Problems to be solved by the invention] By the way, the pilot injection amount of the pilot injection device is
It is determined by the dynamic valve opening pressure of the accumulation rate piston used as a pressure relief member. That is, when the dynamic valve opening pressure falls below a predetermined pressure, the pilot injection amount decreases. It is known that this dynamic valve opening pressure decreases when the pressure of the fuel acting on the side surface of the head of the accumulation rate piston at the time of valve opening, that is, the residual pressure of the so-called oil sump filled fuel is high. When the fuel temperature becomes relatively high, the fuel viscosity decreases, so that the oil sump filled fuel easily flows out to the low pressure side through the gap of the sliding portion between the accumulation rate piston and the accumulation rate piston guide. However, the fuel viscosity increases as the fuel temperature decreases. For this reason, when the fuel temperature becomes relatively low, a large viscous force acts on the fuel flowing through the gap of the sliding portion, so that the oil sump filled fuel becomes difficult to flow out to the low pressure side.
As a result, the residual pressure in the oil sump increases, and the dynamic valve opening pressure decreases. Therefore, it has been devised to prevent the fluctuation of the pilot injection amount by drawing out the oil sump filling fuel to the fuel injection pump side via the bypass at the time of non-fuel injection as in the above-mentioned conventional technique.

However, the above-described conventional technique has a complicated bypass hole that opens in the pressure chamber of the fuel injection pump and is intermittently blocked by the plunger, and that a bypass is provided between the bypass hole and the expansion chamber of the pilot injection device. It is a structure. Therefore, when applied to a device that requires reliable operation even under severe environmental conditions such as a decrease in fuel temperature, there is a problem in that the reliability and environmental resistance of the device deteriorate. This lowers the dynamic valve opening pressure of the accumulation rate piston, causes a decrease in the pilot injection amount, or causes obstacles such as inability to perform pilot injection, and it may be difficult to reduce the fuel noise of the diesel engine. It was

Further, it is necessary to add mechanical processing such as a bypass hole, a bypass, and a mechanism for opening and closing the bypass hole by a plunger across both the fuel injection pump and the pilot injection device. Therefore, workability at the time of assembly, maintenance, etc. was deteriorated.

An object of the present invention is to provide a pilot injection device for a fuel injection pump, which can improve the mechanical structure of the pilot injection device only to reduce the residual oil pressure in the oil sump and always perform pilot injection appropriately.

[Means for Solving the Problems] The present invention made in order to achieve the above-mentioned object is to provide an accumulation rate piston guide which communicates with a pressurizing chamber of a fuel injection pump and has a fuel filling section near the communication section, and the accumulation section. A rate piston guide is slidably fitted to the accumulation rate piston that pushes and moves inside the accumulation rate piston guide as the fuel pressure in the pressure chamber rises, and a back pressure chamber that communicates with the accumulation rate piston guide. A pilot injection device for a fuel injection pump, comprising: a biasing member that is internally provided and that generates a biasing force in a direction in which a head side surface of the accumulation rate piston faces closely to the fuel filling section. And a fitting portion between the accumulation rate piston and the fuel filling portion and the back pressure chamber side. In one in which a predetermined amount of fuel is summarized as pilot injector of a fuel injection pump, characterized in that a predetermined gap flowable.

[Operation] In the pilot injection device of the fuel injection pump of the present invention, the accumulation rate piston communicates with the pressurizing chamber of the fuel injection pump and is slidably fitted with the accumulation rate piston guide having the fuel filling section near the communication section. To meet. The accumulation rate piston pushes and moves inside the accumulation rate piston guide as the fuel pressure in the pressurizing chamber rises. On the other hand, the urging member provided in the back pressure chamber that communicates with the accumulation rate piston guide generates an urging force in a direction in which the head side surface of the accumulation rate piston closely faces the fuel filling section. Here, the predetermined gap provided in the fitting portion between the accumulation rate piston guide and the accumulation rate piston functions to allow a predetermined amount of fuel to flow between the fuel filling portion and the back pressure chamber side.

That is, the fuel filled in the fuel filling portion, which is the high pressure side, flows out to the back pressure chamber side, which is the low pressure side, through the predetermined gap provided in the fitting portion between the accumulation rate piston guide and the accumulation rate piston. Of.

Therefore, the pilot injection device of the fuel injection pump of the present invention works to discharge a predetermined amount of fuel from the fuel filling portion through the predetermined gap to the back pressure chamber side to reduce the fuel pressure of the fuel filling portion.

[Embodiment] Next, a preferred embodiment of the present invention will be described in detail with reference to the drawings. FIG. 2 shows a schematic structure of a distribution type fuel injection pump which is one embodiment of the present invention, and FIG. 1 shows a cross section of a pilot injection device which is a main part thereof.

As shown in FIG. 2, the distribution type fuel injection pump 1 includes a vane pump 5 and a drive shaft 3 which are driven by rotation of a drive shaft 3 inside the pump housing 2 to supply pressure to fuel inside the pump chamber 4. A cam plate 6 connected via a coupling, and a plunger 7 that rotates integrally with the cam plate 6 and reciprocates
Is equipped with. The plunger 7 is fitted in the pump cylinder 8 and reciprocates to suck the fuel in the pump chamber 4 from the suction port 9 into the plunger chamber 10 and then pressurize the fuel.
The plunger 7 distributes the fuel pressurized in the plunger chamber 10 to each distribution passage 11 at a predetermined time, and the delivery valve 12
A distribution port 13 for sending pressure to each injection nozzle of a diesel engine (not shown) via a pump chamber 4 for supplying pressurized fuel.
It has a spill port 14 that overflows. A pilot injection device 20 communicating with the plunger chamber 10 is screwed to the pump head 15.

Plunger 7 has a spill ring near spill port 14.
30 is fitted. Depending on the position of the spill ring 30, the fuel pressurization ending timing of the plunger 7, that is, the fuel injection amount is determined. The position of the spill ring 30 is a mechanical governor 31 that controls according to the accelerator operation amount and rotation speed.
And the altitude compensator 32 that performs control according to the atmospheric pressure. The mechanical governor 31 performs the following control. That is, the tension lever 35 is rotated about the fulcrum 36 by the operation of the adjusting lever 33 and the control spring 34 which are linked to an accelerator pedal (not shown). The operation of the tension lever 35 is transmitted to the control lever 38 via the start spring 37, and the position of the spill ring 30 is controlled by the rotation of the control lever 38 around the fulcrum 36. Further, the flyweight 39 attached to the governor main shaft that rotates together with the drive shaft 3 spreads outward due to the centrifugal force according to the rotation speed of the diesel engine. This allows
The governor sleeve 40 presses the control lever 38, and the spill ring is pressed by the control lever 38 as described above.
30 positions are controlled. On the other hand, the altitude compensator 32 controls the position of the spill ring 30 as follows. That is,
The bellows 41 and the push rod 42 move up and down according to the atmospheric pressure. This vertical movement moves the connecting pin 43 left and right, and in response to this movement, the control arm 44, which is the stopper of the tension lever 35, rotates about the fulcrum 45 as an axis. The position of the spill ring 30 is controlled by the tension lever 35 that operates according to the amount of rotation of the control arm 44. Further, the timer mechanism 46 controls the fuel injection timing according to the fuel pressure inside the pump chamber 4.

By the way, the pilot injection device 20 temporarily reduces the fuel pressure inside the plunger chamber 10 during one forward movement of the plunger 7 (pressure feeding stroke) to interrupt the pressure feeding, and after the pilot injection, executes the main injection.

Next, the structure of the pilot injection device 20 will be described with reference to FIG. The pilot injection device 20 communicates with the plunger chamber 10 of the fuel injection pump 1 and is screwed to the body 53, which incorporates the accumulation rate piston guide 52 into which the accumulation rate piston 51 is fitted, and the body 53 through the O-ring 54. It is composed of a cap 55, and an accumulation rate piston stopper 56 interposed between the body 53 and the cap 55.

The body 53 is provided with a screw portion 57 engraved on the outer peripheral surface of the tip so that the body 53 is horizontal with respect to the fuel injection pump 1.
Screwed on. The accumulation rate piston guide 52 communicates with the plunger chamber 10 of the fuel injection pump 1 through the small hole 58 and the communication passage 59, and is closed by a seat portion 60 formed at the tip of the accumulation rate piston 51. 61
Equipped with. The fuel filled in the oil sump 61 exerts a pressure on the side surface of the head of the accumulation rate piston 51. The outer diameter of the seat portion 60 of the accumulation rate piston 51 is formed larger than the inner diameter of the small hole 58. In addition, the rear end of the accumulation rate piston 51, the accumulation rate piston guide
52 and the accumulation rate piston stopper 56
A low pressure chamber 62 is formed.

A back pressure chamber 63 is formed by the body 53, the cap 55, and the accumulation piston stopper 56. Inside the back pressure chamber 63, a pressure pin 64 interlocking with the accumulation rate piston 51 is arranged. Further, a return spring 65 that presses and urges the pressure pin 64 toward the plunger chamber 10 is also incorporated. Further, the back pressure chamber 63 and the fuel injection pump 1 are provided with an accumulation rate piston stopper 56.
Also, they communicate with each other through return passages 66 and 67 formed in the body 53 and a return passage (not shown) formed in the pump cylinder 8. Therefore, the fuel overflowing from the back pressure chamber 63 flows back to the pump chamber 4 on the low pressure side of the fuel injection pump 1 through the return passages 66 and 67. Further, inside the back pressure chamber 63, a pressure pin stopper 68 that restricts the movement amount of the pressure pin 64 is arranged. The pressure pin stopper 68 is configured so that the movement amount of the pressure pin 64 is slightly larger than the movement amount of the accumulation rate piston 51.
Position adjusted by shim 69. Further, the set load of the return spring 65 is set by the adjusting shim 70.
A screw 71 is screwed to the rear end of the cap 55 via a gasket 72.

Next, the operation of the pilot injection device 20 will be described based on FIG. 1 and FIG.

When the plunger 7 of the fuel injection pump 1 rotates and is driven to the right in FIG. 2 following the cam face of the cam plate 6 (pressure feeding stroke), the fuel inside the plunger chamber 10 is pressurized and the plunger 7 Through the distribution port 13 into the distribution passage 11 and is pressure-fed to the injection nozzle of the diesel engine (not shown) through the delivery valve 12. In this way, in the initial stage when the fuel pressure feeding is started, the initial injection of fuel (pilot injection) is performed from the injection nozzle. When the fuel pressure inside the plunger chamber 10 eventually exceeds the urging force of the return spring 65 of the pilot injection device 20 shown in FIG. 1, the accumulation rate piston 51 moves to the right in FIG. 1 and the seat portion 60 is isolated. To do. Then, the pressure receiving area of the accumulation rate piston 51 increases from the head end surface to the tapered side surface of the head, so that the accumulation rate piston 51 rapidly moves to the right in the figure and abuts against the accumulation rate piston stopper 56. Then it stops. As described above, during the movement of the accumulation rate piston 51, the fuel pressure inside the plunger chamber 10 of the fuel injection pump 1 temporarily drops, and the pressure feed of fuel is temporarily stopped. Eventually, when the accumulation rate piston 51 comes into contact with the accumulation rate piston stopper 56 and stops, the fuel is pumped again by the movement of the plunger 7 of the fuel injection pump 1, and the main injection of fuel is executed. At this time, that is, when the accumulation rate piston 51 is in contact with the accumulation rate piston stopper 56, the amount of fuel flowing out from the oil sump 61 is extremely small. Then, the plunger 7 shown in FIG.
When the spill port 14 bored in the plunger 7 is opened by the spill ring 30 by moving to the right of, the fuel in the plunger chamber 10 overflows into the pump chamber 4 and the pressure in the plunger chamber 10 decreases. , The main injection ends. At this time,
Since the pressure in the plunger chamber 10 drops, as shown in FIG. 1, the accelerating force of the return spring 65 causes the accumulation rate piston 51 to return to the position where the seat portion 60 abuts.

By the way, at the moment when the accumulation rate piston 51 opens, the accumulation rate piston of the pilot injection device 20
As shown in FIG. 3, the force acting on 51 is the dynamic valve opening pressure (pressure inside the plunger chamber) P1 of the accumulation rate piston 51, the residual pressure P2 in the oil sump 51, and the head of the accumulation rate piston 51. Partial cross-sectional area (initial pressure receiving area) S1, large-diameter cross-sectional area S2 of the accumulation rate piston 51, return spring 65
Assuming that the setting urging force F is, the following expression (1) can be used.

P1 × S1 + P2 × (S2-S1) −F = 0 (1) By modifying the equation (1) and calculating the dynamic valve opening pressure P1, it can be expressed as the following equation (2).

P1 = F / S1-P2 × (S2 / S1-1) (2) Thus, as the residual pressure P2 in the oil sump 61 increases, the dynamic valve opening pressure P1 of the accumulation rate piston 51 decreases. . Therefore, in order to maintain the dynamic valve opening pressure P1 at or above the predetermined pressure, the fuel remaining in the oil sump 61 is charged with the sliding surface 51a of the accumulation rate piston 51 and the accumulation rate piston guide 52.
Of the low pressure chamber 6 through the clearance between the sliding surface 52a of
2. It is necessary to reduce the residual pressure in the oil sump 61 by causing it to flow out to the back pressure chamber 64.

On the other hand, as shown in FIG. 4, the fuel viscosity increases as the fuel temperature (engine temperature) decreases. Therefore, at low temperatures,
In particular, it becomes difficult for the fuel in the oil sump 61 to flow out. Therefore,
In this embodiment, as shown in FIG. 5, the clearance between the sliding surface 51a of the accumulation rate piston 51 and the sliding surface 52a of the accumulation rate piston guide 52 is enlarged. The size of this clearance will be described in comparison with the clear run of the sliding portion between the nozzle needle and the nozzle body of the injection nozzle of the diesel engine, which has a structure similar to that of the pilot injection device 20. When the air pressure is 2.5 [atm], the leakage amount of air flowing out through the clearance of the injection nozzle is 1
It is about 10 [cc / min]. This clearance is set so as to prevent lubrication mainly by fuel, spraying due to insufficient lubrication of the nozzle needle, and roughness of the sliding surface.
However, in the present embodiment, as shown in FIG. 5, the clearance 73 between the sliding surface 51a of the accumulation rate piston 51 and the sliding surface 52a of the accumulation rate piston guide 52 is changed to the air flow out through the clearance 73. When the leak rate was 2.5 [atm], the amount of leakage increased until it increased to about 75 to 150 [cc / min]. This setting range is set according to the type of fuel and the characteristics required by the engine. The most desirable range (the residual pressure does not become high and a stable injection quantity characteristic is always obtained) is 90 to 120 [ cc / min]. This allows
The fuel remaining in the oil sump 61 positively always flows out to the low pressure chamber 62 and the back pressure chamber 63 through the clearance 73 in a sufficient amount. Further, since the clearance 73 is provided over the entire circumference, between the sliding surfaces 51a, 52a of the accumulation rate piston 51 and the accumulation rate piston guide 52,
Does not cause wear damage. Therefore, the residual pressure P2 inside the oil sump 61 is reduced even when the fuel temperature is low. Therefore, the dynamic valve opening pressure of the accumulation rate piston 51 is
For example, even when the fuel viscosity increases as the fuel temperature (engine temperature) decreases, it can be kept constant at all times. Where the clearance
The size of 73 is, for example, that the flow of viscous fluid between parallel walls is
Based on the fact that it can be expressed as the sum of the linear distribution and the parabolic distribution according to the boundary conditions, the fuel flow rate through the clearance 73 is the same as the predetermined flow rate (for example, the fuel flow rate at high temperature) even when the fuel viscosity increases due to the decrease in fuel temperature. As described above, it is possible to use a boundary condition according to the specifications of the apparatus and to determine by an arithmetic expression.

In this embodiment, the accumulation rate piston guide 52 containing the oil sump 61 is an accumulation rate piston guide, the accumulation rate piston 51 is an accumulation rate piston, and the return spring 65 incorporated in the back pressure chamber 63 is a biasing member. , Respectively.

As described above, according to the present embodiment, the fuel pressure in the oil sump 61 is reduced and the pressure acting on the side surface of the head of the accumulation rate piston 51 is reduced, so that the dynamic valve opening pressure of the accumulation rate piston 51 is reduced. Is maintained at a substantially constant pressure, and a simple mechanical structure enables proper and reliable execution of pilot injection.

That is, as shown in FIG. 5, in the structure of this embodiment,
Clearance between sliding surface 51a of accumulation rate piston 51 and sliding surface 52a of accumulation rate piston guide 52 7
Since 3 is wide enough, the fuel filled in the oil sump 61 flows out to the low pressure chamber 62 and the back pressure chamber 63 through the clearance 73. Therefore, as shown by the solid line in FIG. 6, the amount of leak in the sliding portion having the clearance 73 is almost constant even if the fuel temperature (engine temperature) falls from a high temperature to a low temperature and the fuel viscosity increases. Retained. As a result, the residual pressure of the fuel inside the oil sump 61 is also maintained at a relatively low constant pressure without depending on the fuel temperature.

Further, the dynamic valve opening pressure of the accumulation rate piston 51 (pressure in the plunger chamber when the valve is opened) is almost constant without being affected by the fuel temperature change. Therefore, the pilot injection amount is always guaranteed to be a constant amount even if the fuel temperature (engine temperature) changes. However, in the prior art, as shown by the broken line in the same figure, when the fuel temperature is low, the amount of leak in the sliding portion is small, so the residual pressure inside the oil sump 61 has risen.
Therefore, the dynamic valve opening pressure of the accumulation rate piston was low, and the pilot injection amount was almost 0 or a small amount at low temperature. Therefore, since the fuel temperature is likely to be adversely affected, when the fuel temperature is lowered, the pilot injection amount may be inappropriately small for the operating condition of the diesel engine, or the pilot injection may be impossible.

In this way, the pilot injection suitable for the operating state of the diesel engine can be realized without being adversely affected by the environmental conditions such as the fuel temperature (engine temperature), so that the reliability and environmental resistance of the device are enhanced. Therefore, it is possible to favorably suppress the combustion noise of the diesel engine in the idle operation state and the low speed light load operation state.

In addition, a clearance 73 is provided in the sliding portion between the accumulation rate piston 51 and the accumulation rate piston guide 52, and a sufficiently stable pilot injection that does not depend on environmental conditions such as fuel temperature can be realized with a relatively simple mechanical structure. . Therefore, when the accumulation rate piston 51 slides, uneven wear or the like does not occur on a specific portion of the sliding surface 51a or the sliding surface 52a. Therefore, the durability of the device is further improved.

Further, since the mechanical structure is simple and the outer diameter tolerance of the accumulation rate piston 51 and the inner diameter tolerance of the accumulation rate piston guide 52 only have to be complied with, the manufacturing process can be facilitated by reducing the processing man-hours and improving the work efficiency.

[Effects of the Invention] As described in detail above, the pilot injection device of the fuel injection pump of the present invention is on the high pressure side via the predetermined gap provided in the fitting portion of the accumulation rate piston guide and the accumulation rate piston. The fuel filled in the fuel filling portion is configured to flow out to the back pressure chamber side, which is the low pressure side. For this reason, the fuel pressure in the fuel filling section decreases, and the pressing force acting on the side surface of the accumulation rate piston head decreases due to the filled fuel pressure, so the dynamic valve opening pressure of the accumulation rate piston is maintained at a substantially constant pressure. With the simple mechanical structure, the excellent effect that the optimum pilot injection can always be surely executed is exhibited.

Also, because the execution of proper pilot injection is guaranteed,
The reliability and environment resistance of the equipment are improved, and the combustion noise of the diesel engine can be reduced sufficiently. This is particularly remarkable when the fuel temperature is relatively low, such as when the diesel engine is cold.

Furthermore, since a structure is provided in which a predetermined gap is provided in the fitting portion between the accumulation rate piston guide and the accumulation rate piston, there is no adverse effect such as uneven wear of a specific sliding portion when the accumulation rate piston slides. Durability is also increased.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a pilot injection device according to an embodiment of the present invention, FIG. 2 is a schematic configuration diagram of a fuel injection pump which is also equipped with the pilot injection device, and FIG. 3 is a function of the accumulation rate piston. FIG. 4 is a graph showing the relationship between fuel viscosity and fuel temperature, FIG. 5 is a sectional view of a main part of an embodiment of the present invention, and FIG. It is a graph which shows the relationship with fuel temperature. 1 ... Fuel injection pump, 10 ... Plunger chamber, 20 ... Pilot injection device, 51 ... Accumulation rate piston,
52 …… Accumulate piston guide, 61 …… Oil sump, 63 …… Back pressure chamber, 65 …… Return spring

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Mitsumasa Yamada 1 Toyota Town, Toyota City, Aichi Prefecture Toyota Motor Corporation (72) Inventor Koji Nagata 1-1 Chome Showa Town, Kariya City, Aichi Nihon Denso Co., Ltd. (72) Inventor Zenji Kuwahara, 1-1, Showa-cho, Kariya, Aichi Prefecture, Nihon Denso Co., Ltd. (72) Inventor, Akira Kato, 1-1, Showa-cho, Kariya, Aichi Prefecture, Nihondenso Co., Ltd.

Claims (1)

[Scope of utility model registration request] 1. An accumulation rate piston guide, which communicates with a pressure chamber of a fuel injection pump and has a fuel filling portion near the communication portion, and an accumulation rate piston guide, which is slidably fitted to the accumulation rate piston guide. As the fuel pressure rises, an accumulation rate piston that pushes and moves inside the accumulation rate piston guide and a back pressure chamber that communicates with the accumulation rate piston guide are installed internally, and the head side surface of the accumulation rate piston is the fuel filling portion. And a biasing member that generates a biasing force in a direction to closely face the fuel injection pump, the pilot injection device of the fuel injection pump, and the fuel filling portion at the fitting portion between the accumulation rate piston guide and the accumulation rate piston. A predetermined gap is provided so that a predetermined amount of fuel can flow between the back pressure chamber side and the back pressure chamber side. Pilot injection device for fuel injection pump.